Dynamic Analysis of a Vessel-shaped Fish Farm for Open Sea

Master's thesis in Offshore Technology : Marine and Subsea TechnologyIn recent years, aquaculture has been the fastest-growing animal food producing industry in the world. However, the absence of suitable production areas might potentially become the most limiting factor for future production growth. This motivates and necessitates the development of open sea fish farming. Design of offshore aquaculture systems is a novel and unique engineering challenge, which will depend on numerical tools that can simulate and predict the structural response in open sea conditions. In this master thesis, a vessel-shaped fish farm concept for offshore fish farming is studied. The vessel uses a turret mooring system for station keeping and is designed to break incoming waves and reduce environmental loads on the system. Dynamic analyses have been carried out using numerical simulation programs, with the aim to analyse vessel motions, mooring lines, fish nets, and coupled motions of the system. For studies of the hydrodynamic properties of the vessel, different panel models were created using the design analysis tool GeniE. The RAOs in heave, roll, and pitch were obtained from frequency domain analyses of the vessel hull, using the potential flow solver Wadam. Hydrodynamic data acquired from frequency domain analyses were exported from Wadam to SIMO, the program used for quasi-static time domain analysis of the vessel and simplified mooring system. Based on the mooring lines performance in SIMO, new mooring line parameters were established for the fully coupled time domain simulations in SIMO-Riflex, where fully coupled time domain analyses of the vessel-shaped fish farm was carried out. A sensitivity study was carried out from the fully coupled time domain simulations by comparing three different fish net models; rigid model, flexible model, and flexible model with no reduction factor. It was found that the simplified models overestimate the drag forces on the system, and it is recommended that neither of the simplified models should be used for future dynamic analyses of aquaculture systems. Development of tension in the foremost and rearmost fish nets was studied in steady current conditions, and with a conjunction of regular waves and steady currents. A mutual dependency between the forces on the net and its deformations was found. Motions of the coupled fish farm system and the efficiency of mooring lines were studied in time domain simulations with regular waves and steady currents

Numerical analysis of a vessel-shaped offshore fish farm

The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.acceptedVersio

Numerical Analysis of a Vessel-Shaped Offshore Fish Farm

The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.acceptedVersio